This application makes reference to and claims all benefits accruing under 35 U.S.C. Section 119 from an application for xe2x80x9cAutomatic Gain Control Device of Optical Fiber Amplifier,xe2x80x9d filed in the Korean Industrial Property Office on Jul. 10, 2001 and there duly assigned Serial No. 2001-41157.
1. Field of the Invention
The present invention relates generally to an optical fiber amplifier and, more particularly, to a device for automatically controlling the gain of an optical fiber amplifier.
2. Description of the Related Art
In general, it is not easy to achieve gain flatness and a desired noise figure (NF) among channels in an optical fiber amplifier. In this regard, there has been a need for a gain control device to automatically keep the gains of channels flat despite a variation in the number of input channels or a variation in the intensity of an input optical signal. A conventional gain control method employing optical elements is effective, but has drawbacks in that the construction of an erbium-doped fiber amplifier (EDFA) is complex and difficult to tune the operating parameters of the EDFA to desired conditions based on the position of the EDFA. Another gain control method known in the prior art is achieved by controlling the amount of bias current to a pumping light source to adjust the intensity of pumping light therefrom. However, the optical fiber amplifiers often have different gain characteristics according to the type of pumping light sources, which do not match the gain characteristics desired by a user. For this reason, the user has trouble manually tuning the respective optical fiber amplifiers.
The present invention overcomes the above-described problems, and provides additional advantages by providing an automatic gain control device capable of automatically tuning the optical fiber amplifier to a desired gain value once the value is set by a user.
Accordingly, the automatic gain control device of an optical fiber amplifier includes a first optical detector for partially converting an input optical signal to the optical fiber amplifier into a first electrical signal; a second optical detector for partially converting an output optical signal from the optical fiber amplifier into a second electrical signal; a first programmable amplifier having a first gain value set based on a first control signal for inputting the first electrical signal and amplifying it at the first gain value to output a first amplified signal; a second programmable amplifier having a second gain value set based on a second control signal for inputting the second electrical signal and amplifying it at the second gain value to output a second amplified signal; a proportional-integral derivative (PID) for outputting the compensation signal corresponding to the difference between the power level of the first amplified signal and the power level of the second electrical signal; and, a controller for outputting the second control signal to the second programmable amplifier, such that it has the second gain value based on a third gain value and for varying the first gain value of the first programmable amplifier until the first electrical signal and second amplified signal become the same in the power level, thereby changing the gain value of the optical fiber amplifier to the third gain value.